1. Field of the Invention
The present invention relates to radio devices, and in particular, to an antenna with an active magnetic type antenna with a ferrite core for use in compact media digital radio receivers, for receiving Digital Video Broadcasting (DVB) and radio broadcasting signals, including Digital Multimedia Broadcasting (DMB) in VHF and UHF wave lengths.
2. Description of the Related Art
Digital broadcasting standards, such as DVB and DMB, are being developed, with digital broadcasting networks progressively replacing analog TV and radio in the VHF and UHF frequency bands.
An overwhelming majority of small digital multimedia receivers use a telescopic antenna as their basic antenna. This antenna type is well known and widely used for receiving TV signals and for receiving FM signals in handheld receivers.
Although telescopic antennas are somewhat compact in size in a transportation mode, telescopic antennas have a rather long length in an operating mode. For radio receivers operating at VHF frequency band, e.g. VHF III 170-240 MHz band, now used for the Terrestrial Digital Multimedia Broadcast (T-DMB) standard in several countries, the broadcasting wavelength is too long, and an optimum antenna size can reach up to 450 mm, which is unacceptable from the point of view of a user of a small sized handheld device.
A significant shortcoming of telescopic antennas built in to small-sized multimedia receivers is a mechanical unreliability when in a forward position. The various proposed constructional solutions are equally imperfect from the point of view of large length in the radio signal reception mode, and they easily break during use.
Conventional devices that concern construction of ferrite antennas include Russian Federation Patent Application No. 2006122799, disclosing a ferrite antenna containing a pump oscillator, a ferrite core with first and second reception coils fixedly connected, and a first condenser parallel to the reception coils. The Russian Federation Patent Application discloses a coil independent from a ferrite core with a first output connected to a point on the first and second reception coils. The Russian Federation Patent Application further discloses a semi-conductor diode having an anode connected to a second output of the coil, the transistor having a collector connected to a cathode of the semi-conductor diode, and an emitter of the semi-conductor diode connected to a common point, the coil connected to the pump oscillator and magneto-connected with the coil of inductance. The Russian Federation Patent Application further discloses the switching circuit consisting of the resistor, whose first output is connected to the first output of the coil of inductance, and its second output is connected to the base of the transistor, and the second condenser located between base of the transistor and the common point. However, the device disclosed by the Russian Federation Patent Application increases the complexity of adjustment.
A conventional device having an active magnetic antenna with a ferrite core is described in Pub. No. US 2007/0222695 A1, filed by Steven Jay Davis, the contents of which is incorporated herein by reference. This U.S. Publication conceptually represents the main concept of the electric scheme of this active antenna with the ferrite core, as shown in FIG. 1.
In FIG. 1, a ferrite core 1 of the magnetic antenna operates in conjunction with a winding 2 (Lant) of the frame magnetic antenna and an LC resonance circuit 3 formed by a second winding of the antenna and a variable capacity condenser for antenna resonance trimming, and a Low Noise Amplifier (LNA). As shown in FIG. 1, an antenna having as a main component a ferrite core 1 is provided with windings forming a frame magnetic antenna, with a first winding 2 connected directly to a base 5 of an LNA transistor, making a first resonant contour in a point of a high-frequency feed of the antenna together with a parasitic capacity of base capacitor Cp.
A resonant LC capacitor of resonance circuit 3, magnetically connected to capacitor Cp, contains a second winding and tuning condenser, providing a two-resonant scheme of the antenna, as used in the majority of compact receivers to allow reception the narrow-band antenna for pre-selection of an operating frequency or frequency adjustment of a radio channel.
The frequency band of this antenna is defined by reconstructing contour 3 and a contour 2 of the high-frequency feed of the antenna in good quality, and reconstructing parameters of the transistor 5 and a coefficient of connection between them in good quality. The antenna described in FIG. 1 has an operating bandwidth of about 10-20 kHz at a half-power level and consequently can be used in analog AM radio receivers for reception of long, middle and short radio waves. For digital channel reception such as DMB or DVB, an antenna's operating frequency bandwidth should be not less than 6-8 MHz. The shortcomings of conventional antennas increase when it is necessary to match all frequency bands. For example, using the T-DMB standard, matching will be 66 MHz from 174 Mhz up to 240 MHz, and 392 MHz bandwidth will used for a DVB-Handheld (DVB-H) standard of 470 Mhz-862 MHz. For so wide operating frequency bandwidth (more than 30%) the antennas which will meet that requirement can be arranged as Ultra-Wide Band (UWB).
Further, a mathematical simulation of the two-resonance circuit solution described above by HFSS™ software demonstrated that there are no improvements in antenna gain compared to a non-resonance ferrite core antenna, with an operating bandwidth determined by antenna gain suppression out of the resonance zone and all attempts to expand the antenna's operating frequency bandwidth are for antenna gain degradation only.
Among the problems solved by present invention is providing a more compact active magnetic antenna having a ferrite core with increased sensitivity, capable of accepting a broadband digital signal without conceding beneficial large telescopic antenna characteristics.